The present invention relates to a method and apparatus for delivering a therapeutic agent to a localized internal tissue site within a patient. While various techniques are presently known in the prior art for such localized delivery of a therapeutic agent, a disadvantage in such techniques often exists in that the presence of the therapeutic agent is often transient. The agent is typically washed away by moving fluids within the body, or quickly neutralized by biochemical processes.
Techniques are known to the art for the localized delivery of therapeutic agent by means of a small catheter which extends from the exterior of the patient to the internal tissue site, with a mechanical delivery system being provided to administer the therapeutic agent in a continuous, or periodic, controlled dosage over a substantial period of time. However, this requires the continuing presence of the catheter in the body, and the patient remains connected to the mechanical controlled delivery mechanism.
As another technique, controlled release members are surgically implanted into the patient, for example a plastic mass in which the therapeutic agent is impregnated. Such a controlled release member provides desired controlled release of a therapeutic agent, but the plastic carrier member remains as an implant after the therapeutic agent has been exhausted, unless it is removed, which may require surgery.
In accordance with this invention, a new method and apparatus for delivering therapeutic agent is provided, preferably for delivery in a controlled release manner over a substantial period of time at the internal tissue site. Thus, the internal tissue site can be bathed in the therapeutic agent for such a substantial period of time without the necessary presence of an indwelling catheter, and preferably without the presence of a residual implant which must be later removed.
The method of this invention may be performed in conjunction with other medical procedures. For example, it may be performed in conjunction with the well known PTCA procedure pertaining to the balloon dilation of coronary arteries to improve blood flow. It is the current custom in a PTCA procedure or related procedures to deliver by injection up to about 10,000 units of heparin as a bolus during or immediately after the procedure, with hourly or additional doses of heparin being administered up to 24 hours after the PTCA procedure.
However, it is known that such a systemic delivery of heparin has significant potential side effects that may contraindicate the PTCA procedure for certain patients i.e., those who are subject to internal bleeding such as ulcer patients, or patients with high blood pressure.
The purpose of providing a dosage of heparin to the patient immediately after PTCA or the like is to prevent the clotting of blood at the site where the artery was dilated by the balloon catheter in the procedure. By this invention, it becomes possible to administer overall a much lower effective dosage of heparin by administering it locally at the site of the arterial stenosis which was dilated by the balloon catheter. This is done by the application of heparin or other therapeutic agent directly to the stenosis site. Preferably, the therapeutic agent so applied can exhibit a controlled release characteristic for a long, effective life even after the PTCA catheter has been withdrawn.
Additionally, one in three patients conventionally have a restenosis within six months at the same arterial site, so that the coronary artery occludes once again, often putting the patient into worse condition than he was before the original PTCA procedure. In accordance with this invention it is possible during the original PTCA procedure to provide slow release therapeutic agents that reside in and adjacent the tissue of the stenosis to suppress not only thrombosis, but also subintimal fibromuscular hyperplasia, resulting in regrowth of the stenosis.
The invention of this application can be used in a wide variety of medical procedures above and beyond the dilation of stenoses in coronary arteries. One may provide therapeutic agents to a variety of internal tissue sites where such is needed, preferably resulting in a persistent dosage of medication at the site. The medication and carrier, when used, is preferably removed by biochemical processes to leave no significant residue at the internal tissue site.